Method of forming a writer with an AFM write gap

ABSTRACT

A perpendicular magnetic recording (PMR) head is fabricated with main pole and a trailing edge shield antiferromagnetically coupled across a write gap by either having the write gap layer formed as a synthetic antiferromagnetic tri-layer (SAF) or formed as a monolithic layer of antiferromagnetic material. The coupling improves the write performance of the writer by enhancing the perpendicular component of the write field and its gradient. Methods of fabricating the writer are provided.

This is a Divisional Application of U.S. patent application Ser. No.13/068,638, filed on May 16, 2011, which is herein incorporated byreference in its entirety and assigned to a common assignee.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the fabrication of a perpendicular magneticrecording (PMR) write head whose main pole is at least partiallysurrounded by shields formed of magnetic material. In particular itrelates to such a head whose main pole and trailing shield is separatedby a write gap formed of antiferromagnetic (AFM) material.

2. Description of the Related Art

The increasing need for high recording area densities (up to 1 Tb/in²)is making the perpendicular magnetic recording head (PMR head) areplacement of choice for the longitudinal magnetic recording head (LMRhead).

By means of fringing magnetic fields that extend between two emergingpole pieces, longitudinal recording heads form small magnetic domainswithin the surface plane of the magnetic medium (hard disk). As recordedarea densities are required to increase, these domains mustcorrespondingly decrease in size, eventually permitting destabilizingthermal effects to become stronger than the magnetic interactions thattend to stabilize the domain formations. This occurrence is theso-called superparamagnetic limit. Recording media that acceptperpendicular magnetic recording, allow domain structures to be formedwithin a magnetic layer, perpendicular to the disk surface, while a softmagnetic underlayer (SUL) formed beneath the magnetic layer acts as astabilizing influence on these perpendicular domain structures. Thus, amagnetic recording head that produces a field capable of forming domainsperpendicular to a disk surface, when used in conjunction with suchperpendicular recording media, is able to produce a stable recordingwith a much higher area density than is possible using standardlongitudinal recording.

Since their first use, the PMR head has evolved through severalgenerations. Initially, the PMR head was a monopole, but that design wasreplaced by a shielded head design with a trailing edge shield (TS),which, due to its negative field, provides a high field gradient in thedown-track direction to facilitate recording at high linear densities.

Side shields (SS) then began to be used in conjunction with the trailingedge shields, because it was necessary to eliminate the fringing sidefields in order to increase writing density still further.Unfortunately, despite the benefits they provided, the presence of theseshields inevitably reduces the field produced by the main pole becausethe basis of their operation is the removal of portions of the flux ofthat field. Therefore, as long as design functionalities can beachieved, it is important to reduce any additional flux shunting by theshields from the main pole. This is a particularly importantconsideration for future PMR writer designs which utilize increasinglysmall pole tips.

In today's quest for very high density magnetic recording it isessential to improve the bit error rate (BER). This requires an increasein the recorded bits per inch (BPI) As the data rate for writingincreasing rapidly to the GHz range, it is also important to increasethe data rate capability of the writer without losing the BER. Attoday's state-of-the-art rate of 750 Gb/in² areal density, the physicalwidth of the writer is reduced to only ≈50 nm (nanometers), with a writegap reduced to sub-30 nm dimensions. The reduction of writer dimensionsposes a significant challenge to maintain the write field strength andfield gradient for OW, BER and adequate frequency response. This isbecause most of the writing flux will be shunted from the main pole tothe trailing shield without there being an adequate magnetizationcomponent along the direction that is vertical to the ABS plane. Acritical aspect of writer design, therefore, is to achieve the highwriting field and high field gradient by engineering the magnetizationconfiguration and response of the main pole and trailing shield region.

Referring first to schematic FIG. 1, there is shown a sidecross-sectional view of components of a prior art PMR write head, withits ABS end (dashed line (60)) positioned over a perpendicular recordingtype magnetic medium (100) having a magnetically soft underlayer (SUL)(150). There is shown a lead shield (80), a main pole (20), a trailingshield (40), a write gap (65) between the main pole and the trailingshield and a yoke (90). Note that these components generally projectbackwards (away from the ABS) so that the yoke and main pole have aclosed configuration, but that extended view is not shown here. Thetrailing shield (40) is grown on a high magnetic moment (high Ms) seedlayer (45). The medium (100) is moving from the lead shield towards thetrailing shield.

During writing, magnetic flux (10) emerges from the main pole (20) andtakes two paths. A first path (30) is directly shunted to the trailingshield (40) through the write gap (65), which drives the magnetizationof the trailing shield (50) to be parallel to the ABS (60) of thewriter. Since the medium is responsive to a vertical field, this fluxcomponent is not useful for writing and it should be reduced. Anotherflux path (35) emerges from the pole tip, passes through the softmagnetic under layer (SUL) (150) at the bottom of the magnetic mediumand returns to the trailing shield (40). This component of the flux isthe one actually doing the writing on the medium. For good writeperformance the flux emerging from the main pole and entering the mediumneeds to have a strong vertical (perpendicular to the ABS) component andit should have some vertical component relative to its re-entrance intothe ABS of the trailing shield to efficiently close the flux loop.Therefore, it is advantageous to increase the vertical magnetization ofboth the main pole and the trailing shield adjacent to the write gap.

The effects of the write field of a prior art configuration such as thatshown in FIG. 1 can be obtained from the graph shown in FIG. 2. Thegraph of FIG. 2 is a micromagnetic modeling result showing the magnitudeprofile of a down-track write field, as a function of elapsed time afterwrite-current switching. The magnitude, H_(eff) is measured in Oe alongthe graph ordinate and the down-track position is measured along theabscissa in microns (μm) down track from the pole tip. Five measurementtimes are superimposed, from 0.5 ns (nanoseconds) to 2.5 ns after thefield is shut off.

Two conclusions can be drawn from the graph.

1) the trailing shield magnetization response is lagging behind the mainpole field and,

2) the maximum field gradient depends on the positive and negative peakvalues of H_(eff) and their spacing.

In this modeling experiment, the magnetization of the trailing shieldhas a component in the same direction as that of the main pole, fromtimes of 0.5 to 1.5 ns, as evidenced by the same polarity of the writingfield under the trailing shield. Beginning at 2 ns, however, thistrailing shield flux polarity switches direction, providing someanti-parallel component to the main pole magnetization and, thereby,generating a negative dip in the field profile which produces a highfield gradient. This effect is greatest at 2 ns and 2.5 ns where theswitch in polarity of the field from an H_(eff) of approximately 17 kOeto an H_(eff) of approximately −5 kOe (opposite direction) is due tosome component of the trailing shield flux which is anti-parallel to theflux emerging from the pole tip.

These results imply that it will be advantageous to have a writer designwhich enhances the flux component perpendicular to the ABS between themain pole and the trailing shield that thereby enhances the write fieldstrength and the field gradient. We shall use syntheticantiferromagnetically (SAF) coupled multilayer structures andintrinsically antiferromagnetic materials to achieve the desired designproperties. Such structures have appeared in the prior art, but have notbeen used as in the present invention. Examples can be found in Kief etal. (U.S. Publ. Pat. Appl. 2010/0214692), Van der Heijden et al. (U.S.Pat. No. 6,813,115), Zhang et al. (U.S. Publ. Pat Appl. 2010/0119874,assigned to the present assignee) and Tagami et al. (U.S. Pat. No.7,443,633).

SUMMARY OF THE INVENTION

A first object of this invention, therefore, is to design and fabricatea PMR writer with a main pole and shield configuration having animproved performance.

A second object of the present invention is to design and fabricate sucha PMR writer with a main pole and trailing shield configuration thatenhances the write field strength and field gradient of the shieldedpole.

A third object of the present invention is to design and fabricate sucha PMR writer with a main pole and trailing shield configuration thatenhances the direction of the write field perpendicularly to the ABS ofthe writer.

A fourth object of the present invention is to satisfy the first twoobjects with a main pole and trailing shield configuration that ismagnetically coupled in a manner that promotes an anti-parallelorientation of their magnetizations.

These objects will be met by a writer design and its method offabrication in which an anti-parallel coupling is formed between themain pole, the trailing shield and an antiferromagnetic material thatfills the write gap between them. More specifically, designs andstructures will be provided in which the usual paramagnetic write gapmaterial is, in one embodiment, replaced by a syntheticanti-ferromagnetic (SAF) multilayer which provides such an anti-parallelcoupling. In another embodiment, the usual paramagnetic write gapmaterial is replaced by a monolithic layer of intrinsicallyantiferromagnetic material. In each case, the material filling the writegap enables the desired anti-parallel coupling of the magnetizations ofthe pole, the trailing shield and the write gap material. This couplingthen directs the write field to be aligned with the magnetization of thewrite gap structure, which enhances its component perpendicular to theABS as is desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view, perpendicular to the ABSplane, of a prior art PMR writer having a main pole tip shielded on atrailing side and a leading side, showing the flux paths through amagnetic medium having a soft magnetic underlayer (SUL).

FIG. 2 is a graphical representation showing the down-track write-fieldprofile of the prior art writer of FIG. 1 at different times afterswitching of the write current.

FIG. 3 is a schematic cross-sectional view, perpendicular to the ABSplane, of a first embodiment of the present PMR in which the write gapbetween the main pole and the trailing shield is filled with a syntheticanti-ferromagnetically coupled structure.

FIG. 4 is a schematic cross-sectional view, perpendicular to the ABSplane, of a second embodiment of the present PMR in which the write gapbetween the main pole and the trailing shield is filled with anintrinsically antiferromagnetic material.

FIGS. 5a-5h are a sequence of schematic cross-sectional views, thefigures providing, in succession, both a front (ABS) and a sidecross-section, illustrating the process steps by which the embodimentsof FIG. 3 and FIG. 4 can be fabricated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The two embodiments of the present invention described herein are each aPMR writer with a main pole and trailing shield configuration whosemagnetizations are coupled by means of a write gap filling material, toproduce a system with anti-parallel magnetizations. In one embodiment awrite gap filling material that is a synthetic anti-ferromagneticallycoupled multi-layered structure (a SAFS) provides the desired couplingbetween the pole and shield. In another embodiment, a write gap fillingmaterial that is a monolithic layer of intrinsically antiferromagneticmaterial provides the coupling. In each case the antiferromagneticcoupling constrains the magnetic write field to be parallel to thedeposition layer plane of the write gap filling material, therebyenhancing the write field component in a direction perpendicular to themagnetic recording medium. A process for forming these embodiments isalso provided.

First Embodiment

In a first embodiment of the present writer design; which is illustratedin schematic FIG. 3, there is shown a main pole (20), denoted MP, atrailing write shield (40), denoted WS, and a write gap (65), denotedSAF-WG, because it will be filled with an SAF structure as discussedbelow. The trailing write shield (40) is grown on a high magnetic moment(high Ms) seed layer (45), denoted HS. A dashed line (60) denotes theABS surface of the structure.

A possible SAF system to fill the write gap and provide theanti-parallel coupling between shield and pole could be a tri-layerformed as:

Ferromagnetic/Ru, Rh, Cr, Cu/Ferromagnetic

Wherein two layers of ferromagnetic material are anti-ferromagneticallyexchange coupled across a layer of transition metal, such as Ru, Rh, Cr,or Cu. However, special ferromagnetic material will be needed in thisapplication since the strong gap field from the main pole to thetrailing shield can overcome the anti-ferromagnetic coupling strengthprovided by a Ru layer. Hence the magnetization of the ferromagneticlayers in the SAF tri-layer will align with the gap field and shunt thewrite flux. The magnetizations of the ferromagnetic layers in the SAFmust remain anti-parallel to each other in the film plane of the layersin the presence of a strong gap field. A material with a strong negativeanisotropy, like Co₈₀Ir₂₀ (the subscripts referring to atom-percentagesin the alloy) which has a strong enough anisotropy to prevent anout-of-plane orientation, is an ideal candidate for the SAFferromagnetic layer material. The Co₈₀Ir₂₀ material has anisotropyK=−7×10⁷ erg/cc and Ms=12,000 emu, which yields Hk=2 K/Ms≈6000 Oe.

Referring back to FIG. 3, the write gap (65) is shown filled with twocontiguous tri-layers (200), (300), separated by a layer of Ru (400).Each of the two tri-layers comprises a first ferromagnetic layer ofanisotropic ferromagnetic material (210) and (310), such as Co₈₀Ir₂₀,respectively, an intermediate layer of Ru (220), and (320) respectivelyand a second ferromagnetic layer of anisotropic ferromagnetic material,such as Co₈₀Ir₂₀, (230), (330) respectively. The first and secondferromagnetic layers of each tri-layer are coupled with anti-parallelmagnetizations (arrows). Layer (210) of SAF tri-layer (200) promotes amagnetization (arrow (410)) in the main pole (20) that is parallel tothe magnetization of layer (210). The magnetization of layer (330) ofSAF tri-layer (300) promotes a parallel magnetization (500) in the seedlayer (45) on which it is formed. Preferred choices for theferromagnetic material is an anisotropic CoIr alloy (eg. Co₈₀Ir₂₀) orother Co, Fe, Ni alloy. For the intermediate layer, the materials Ru,Rh, Cr, Cu or Au are preferred. The directions of the magnetizations(500) and (410) are now the directions desired to enhance the componentof the write field that is perpendicular to the ABS

Second Embodiment

Referring now to schematic FIG. 4, there is shown a shielded pole designin all other ways identical to that of FIG. 3 except that the SAFtri-layers filling the write gap (65) in FIG. 3 are here replaced by amonolithic layer of intrinsically antiferromagnetic material (hence, anAFM-WG), such as PtMn, NiMn, OsMn, NiCrMn, FeMn, NiO, CoO or NiCrO. Ascan be seen by the configuration of anti-parallel magnetization arrows(650), the effect of the antiferromagnetic layer is to couple themagnetizations (500), (410) of the write shield and the main pole in ananti-parallel direction so that their components perpendicular to theABS are enhanced.

Fabrication Method

The designs described above as first and second preferred embodimentscan both be implemented by the following process steps.

Referring first to schematic FIG. 5a , there is shown in a frontcross-sectional, ABS view, the ABS of the milled pole tip (25) of aplated main pole. The pole is shown as partially surrounded by a seedlayer (15) and by a leading edge magnetic shield (80), also surroundedby its seed layer (85).

Referring next to schematic FIG. 5b , there is shown a sidecross-sectional view of the configuration of FIG. 5a . The furtherextent of the main pole (20) away from the ABS is shown as well as themilled taper (27) on its trailing edge surface.

Referring next to schematic FIG. 5c , there is shown a front ABScross-sectional view of the fabrication of FIGS. 5a and 5b , furtherincluding a deposited write gap layer (65) formed to a thickness ofbetween approximately 150 angstroms to 350 angstroms, as either the SAFtri-layers of the first embodiment (FIG. 3) or as the monolithicintrinsically antiferromagnetic layer of the second embodiment (FIG. 4).A thin, seed layer of the trailing shield material (40) is deposited onthe write gap layer.

Referring next to schematic FIG. 5d , there is shown the fabrication ofFIG. 5c in a side cross-sectional view.

Referring next to schematic FIG. 5e , there is shown a front ABScross-sectional view of the fabrication of FIG. 5c , now also includingthe deposition of a sacrificial layer of hard magnetic material (90) onthe layer of trailing shield material (40). The layer of hard magneticmaterial can be a layer of Co, Fe, Ni or alloys such as CoPt, FePt,formed to a thickness of between approximately 10 angstroms and 200angstroms.

Layers (40) and (90) are exchange coupled. Then a strong field,typically 1 Tesla, which is higher than He of the hard magnetic layer(90), which is typically approximately 5000 Oe, is applied to set themagnetization (arrow (94)) of the hard magnetic layer as well as themagnetization (arrow (44)) of the shield layer (40) beneath it alongthat same direction, whereby the magnetization of the hard magneticlayer pins the magnetization of the shield layer. Then a small field isapplied to set the magnetization of the main pole (arrow (27)) in adirection opposite to that set in (40) and (90), the field being smallenough, typically between approximately 50 and 1000 Oe, to not affectthe previously set magnetizations of (40) and (90) and to be permittedto remain on during subsequent cooling. The fabrication is then annealedat a temperature above the blocking temperature of the monolithicintrinsic AFM layer or the multi-layer, synthetic SAF write gap layer(65) and allowed to cool down, whereupon the magnetizations of the mainpole (arrow (27)) and shield (40) will be coupled in anti-paralleldirections to the write gap layer (65).

Referring to schematic FIG. 5f , there is shown a side view of FIG. 5e ,where the magnetization arrows (44) and (94) are shown as entering thefigure plane (X in a circle), while the magnetization of the main pole(27) is shown as an arrow coming out of the figure plane (dot incircle). Finally, the sacrificial hard magnetic layer (90) is milledaway and the remainder of the fabrication proceeds in a known mannersuch as by plating to form the remainder of the trailing shield.

Alternative Fabrication Method

Referring next to schematic FIG. 5g , there is shown an ABScross-sectional view of the results of an alternative method (thatbegins with the fabrication of FIG. 5c ) for achieving the results ofthe previous fabrication. In this method, a sacrificial layer of Ru (88)is deposited on the thin trailing shield material layer (40) of FIG. 5cand, over the Ru layer, there is then deposited a ferromagnetic layer(90), which will also be a sacrificial layer. The product of themagnetic moment and thickness of this ferromagnetic layer (90) isgreater than that of the trailing shield layer (40). This forms asynthetic antiferromagnetic (SAF) tri-layer comprising the three layers[(90)(88)(40)]: the trailing shield layer (40), the Ru layer (88) andthe ferromagnetic layer (90). A small magnetic field, betweenapproximately 50 and 1000 Oe, is then applied to set the magnetization(arrow (44)) of the trailing shield layer (40), following which the AFMor SAF write gap layer (65) is annealed at an annealing temperaturewhile the small field is on and then the annealing temperature isreduced to the point of elimination, leaving the main pole (25)magnetization (arrow (27)) and the trailing shield layer (40)magnetization (arrow (44)) coupled in anti-parallel directions. Thesacrificial ferromagnetic layer (90) is also magnetized (94) and coupledacross the Ru layer (88) to the shield layer (40). The ferromagneticlayer (90) and the Ru layer (88) are then removed by milling, leavingthe shield layer (40) exposed to act as a seed layer on which tocomplete a plating formation of an entire trailing shield (not shown).

Referring finally to schematic FIG. 5h , there is shown the fabricationof FIG. 5g in a side cross-sectional view, where the magnetizationarrows (94) and (44) of the SAF tri-layer (90)(88)(40) are shown inanti-parallel directions and the magnetization (27) of the main pole(25) is anti-parallel to the shield layer magnetization (44).

As is understood by a person skilled in the art, the preferredembodiments of the present invention are illustrative of the presentinvention rather than limiting of the present invention. Revisions andmodifications may be made to methods, materials, structures anddimensions employed in forming and providing a PMR head having a mainpole and trailing edge shield separated by a material havingantiferromagnetic properties, while still forming and providing such aPMR head and its method of formation in accord with the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. A method of fabricating a PMR head, comprising:providing a main pole having a tapered tip with an ABS end and atrailing edge surface; forming on the trailing edge surface of said mainpole an antiferromagnetic write gap layer; forming on saidantiferromagnetic write gap layer, on a high Ms seed layer, a thin layerof shield material; forming on said layer of shield material asacrificial layer of hard magnetic material; applying a first magneticfield to form in-layer parallel exchange coupled magnetizations of saidlayer of shield material and said sacrificial layer of magneticmaterial, said hard magnetic layer pinning the magnetization of saidlayer of shield material and both said magnetizations having a directionin said ABS plane; while applying a second magnetic field and at anannealing temperature, setting a magnetization of said main pole in adirection opposite to said magnetizations of said shield material andsaid sacrificial layer of magnetic material and coupling said main polemagnetization antiferromagnetically to said layer of shield material bymeans of said antiferromagnetic write gap layer; milling away saidsacrificial layer; completing a formation of a trailing shield on saidthin layer of shield material.
 2. The method of claim 1 wherein saidfirst magnetic field exceeds Hc for said sacrificial layer of hardmagnetic material.
 3. The method of claim 2 wherein said first magneticfield is approximately 1 T and said Hc is approximately 5000 Oe.
 4. Themethod of claim 1 wherein said second magnetic field is small enough toleave unchanged previously set magnetizations of said shield materialand said sacrificial layer of hard magnetic material.
 5. The method ofclaim 4 wherein said second magnetic field is between approximately 50and 1000 Oe.
 6. The method of claim 1 wherein said write gap layer isbetween approximately 150 angstroms and 350 angstroms in thickness. 7.The method of claim 1 wherein said write gap layer is a SAF tri-layercomprising a layer of Ru, Rh, Cr, Cu or Au, sandwiched on both sides bysubstantially identically layers of the anisotropic ferromagneticmaterial Co₈₀Ir₂₀ or another alloy of Co, Fe and Ni.
 8. The method ofclaim 1 wherein said write gap layer is a layer of the antiferromagneticmaterial PtMn, NiMn, OsMn, NiMn, NiCrMn, IrMn, FeMn, NiO, CoO or NiCoO.9. A method of fabricating a PMR head, comprising: providing a main polehaving a tapered tip with an ABS end and a trailing edge surface;forming on the trailing edge surface of said main pole anantiferromagnetic write gap layer; forming on said antiferromagneticwrite gap layer a layer of trailing shield material; forming on saidlayer of trailing shield material a sacrificial layer of Ru; forming onsaid sacrificial layer of Ru a sacrificial layer of hard magneticmaterial whereby said tri-layer comprising said layer of hard magneticmaterial, said layer of Ru and said layer of trailing shield materialform a synthetic antiferromagnetic layer; while applying an annealingtemperature to anneal said antiferromagnetic write gap layer, applying amagnetic field to magnetize said layer of shield material; whilemaintaining said magnetic field, cooling down said annealing temperatureleaving said layer of trailing shield material and said magnetic polemagnetized in anti-parallel directions and maintained in thatconfiguration by said antiferromagnetic write gap layer; milling awaysaid sacrificial layers of Ru and of said hard magnetic material;completing a formation of a trailing shield on said layer of shieldmaterial.
 10. The method of claim 9 wherein said sacrificial layer ofhard magnetic material has a product of its magnetic moment and itsthickness that is higher than that of said layer of shield material. 11.The method of claim 9 wherein said write gap layer is at least one SAFtri-layer comprising a layer of Ru, Rh, Cr, Cu or Au, sandwiched on bothsides by substantially identically layers of the anisotropicferromagnetic material Co₈₀Ir₂₀ or another alloy of Co, Fe and Ni. 12.The method of claim 9 wherein said write gap layer is a layer of theantiferromagnetic material PtMn, NiMn, OsMn, NiMn, NiCrMn, IrMn, FeMn,NiO, CoO or NiCoO.
 13. The method of claim 9 wherein said write gaplayer is between approximately 150 angstroms and 350 angstroms inthickness.
 14. The method of claim 9 wherein said magnetic field isbetween approximately 50 and 1000 Oe.